1. Field of the Invention
The invention relates to a vehicle steering system and a vehicle steering method.
2. Description of Related Art
There is known an electric power steering (EPS) as a vehicle steering system of this type (for example, see U.S. Pat. No. 5,198,981). The electric power steering executes reaction force control in which a target steering reaction force (or a target steering torque) to be applied to a steering wheel is set on the basis of a steering angle and a vehicle speed and then the target steering reaction force is applied to the steering wheel. By executing such reaction force control, it is possible to improve driver's steering feeling. Other than the above, there are Japanese Patent Application Publication No. 06-056046 (JP 06-056046 A) and Japanese Patent Application Publication No. 2006-137215 (JP 2006-137215 A) as related art documents related to the invention.
Incidentally, a steering mode of a steering wheel includes two modes, that is, turn steering and return steering. In the turn steering, the steering wheel is steered in a direction to increase the absolute value of a steered angle of steered wheels (for example, front wheels). In the return steering, the steering wheel is steered in a direction to reduce the absolute value of the steered angle of the steered wheels. However, in the technique described in the U.S. Pat. No. 5,198,981, for example, it is not taken into consideration whether the steering mode of the steering wheel is turn steering or return steering, and a target steering reaction force is uniformly set on the basis of the steering angle. Therefore, for example, depending on the steering mode of the steering wheel, a feeling of strangeness may be experienced by a driver. As a result, there is a technical problem that it may be difficult to improve driver's steering feeling.